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How to wipe a file

   

Here is a nice method to wipe a file as many times as you want.

procedure WipeFile(
  const FileName: String; (* file to be wiped *)
  const Times: Integer = 1 (* how many times ? *)
  );
type
  (* wipe 4kb at a time *)
  TBuffer = array[0..4095] of Byte;
  (* size of TBuffer *)
const
  szBuffer = sizeof(TBuffer);
var
  (* we need to know how many bytes we have left *)
  BytesLeft,
  (* this is to know how bytes we write *)
  BufferSize: Int64;
  (* a buffer variable *)
  buffer: TBuffer;
  index: Integer;
  (* we use a file stream to overwrite the file *)
  theFile: TFileStream;
begin
  (* open the file *)
  theFile := TFilestream.Create(FileName, fmOpenReadWrite or fmShareExclusive);
  try
    (* fill buffer with 128 values *)
    FillChar(buffer, szBuffer, 128);
    (* how many times should we wipe it ? *)
    for index := 1 to Times do begin
      (* remaining bytes *)
      BytesLeft := theFile.Size;
      (* start/restart from the beginning of the file *)
      theFile.Position := 0;
      (* while not end-of-file... *)
      while BytesLeft > 0 do begin
        (* check how many bytes we have left *)
        if BytesLeft > szBuffer then
          (* if we have more than 4096 bytes left
            then we only wipe 4096 bytes this time *)
          BufferSize := szBuffer else
          (* we have 4096 or less bytes left *)
          BufferSize := BytesLeft;
        (* overwrite the file(wipe) *)
        theFile.WriteBuffer(Buffer, BufferSize);
        (* update BytesLeft variable *)
        BytesLeft := BytesLeft -BufferSize;
      end;
    end;
  finally
    (* free the file stream *)
    FreeAndNil(theFile);
  end;
  (* ...finally delete the file, it should not be
    possible to *undelete* it *)
  Deletefile(FileName);
end;
Author: Dorin Duminica
Contributor: Riccardo Faiella (Topellina)
Added: 2012-07-06
Last updated: 2012-07-06

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